Tuesday, May 30, 2017

The orbits of two stars, S0-2 and S0-38 located near the Milky Way’s supermassive black hole will be used to test Einstein’s theory of General Relativity and potentially generate new gravitational models. Image Credit: . SAKAI/A.GHEZ/W.M. Keck Observatory/ UCLA Galactic Center Group.

W. M. Keck Observatory Data Leads To First Of Its Kind Test of Einstein’s Theory of General Relativity

A UCLA-led team has discovered a new way of
probing the hypothetical fifth force of nature using two decades of observations
at W. M. Keck Observatory, the world’s most scientifically productive
ground-based telescope.

There
are four known forces in the universe: electromagnetic force, strong nuclear
force, weak nuclear force, and gravitational force. Physicists know how to make
the first three work together, but gravity is the odd one out. For decades,
there have been theories that a fifth force ties gravity to the others, but no
one has been able to prove it thus far.

“This
is really exciting. It’s taken us 20 years to get here, but now our work on
studying stars at the center of our galaxy is opening up a new method of
looking at how gravity works,” said Andrea Ghez, Director of the UCLA Galactic Center Group and co-author of the study.

Ghez
and her co-workers analyzed extremely sharp images of the center of our galaxy
taken with Keck Observatory’s adaptive optics (AO). Ghez used this cutting-edge
system to track the orbits of stars near the supermassive black hole located at
the center of the Milky Way. Their stellar path, driven by gravity created from
the supermassive black hole, could give clues to the fifth force.

“By
watching the stars move over 20 years using very precise measurements taken
from Keck Observatory data, you can see and put constraints on how gravity
works. If gravitation is driven by something other than Einstein’s theory of
General Relativity, you’ll see small variations in the orbital paths of the
stars,” said Ghez.

This is the first time the
fifth force theory has been tested in a strong gravitational field such as the
one created by the supermassive black hole at the center of the Milky Way. Historically,
measurements of our solar system’s gravity created by our sun have been used to
try and detect the fifth force, but that has proven difficult because its
gravitational field is relatively weak.

“It’s exciting that we can
do this because we can ask a very fundamental question – how does gravity
work?” said Ghez. “Einstein’s theory describes it beautifully well, but there’s
lots of evidence showing the theory has holes. The mere existence of
supermassive black holes tells us that our current theories of how the universe
works are inadequate to explain what a black hole is.”

Ghez and her
team, including lead author Aurelien Hees and co-author Tuan Do, both of UCLA,
are looking forward to summer of 2018. That is when the star S0-2 will be at
its closest distance to our galaxy’s supermassive black hole. This will allow
the team to witness the star being pulled at maximum gravitational strength – a
point where any deviations to Einstein’s theory is expected to be the greatest.

About
Adaptive Optics

W. M. Keck Observatory is a
distinguished leader in the field of adaptive optics (AO), a breakthrough
technology that removes the distortions caused by the turbulence in the Earth’s
atmosphere. Keck Observatory pioneered the astronomical use of both
natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and our
current systems now deliver images three to four times sharper than the Hubble
Space Telescope. AO has
imaged the four massive planets orbiting the star HR8799, measured the mass of
the giant black hole at the center of our Milky Way Galaxy, discovered new
supernovae in distant galaxies, and identified the specific stars that were
their progenitors.

About W. M. Keck Observatory

The W. M. Keck
Observatory operates the largest, most scientifically productive telescopes on
Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea
on the Island of Hawaii feature a suite of advanced instruments including
imagers, multi-object spectrographs, high-resolution spectrographs, integral-field
spectrometers, and world-leading laser guide star adaptive optics systems. The
Observatory is a private 501(c) 3 non-profit organization and a scientific
partnership of the California Institute of Technology, the University of
California, and NASA.